1. Field of the Invention
The invention relates to an implantable medical apparatus for stimulating a heart, of the type having a stimulation pulse generator which generates and delivers stimulation pulses, a detector which, when activated, detects spontaneous heart events and a control device which controls the stimulation pulse generator and the detector, which apparatus for inducing or terminating a tachyarrhythmia delivers a sequence consisting of a predetermined number of stimulation pulses with a time interval between each stimulation pulse, which sequence is released at a detection of a spontaneous heart event.
2. Description of the Prior Art
An apparatus of the type described above is disclosed in U.S. Pat. No. 4,705,043 which describes a cardioverter/pacemaker. The cardioverter/pacemaker delivers, during an electrophysiology study (EP study) on a heart, a group of stimulation pulses for inducing a tachyarrhythmia. The purpose of inducing the tachyarrhythmia is to determine, under controlled circumstances, the most efficient way of terminating a tachyarrhythmia. The known cardioverter/pacemaker comprises a stimulation pulse generator, a detector for detecting the heart R-waves, a control unit, a transmitting and a receiving unit for radio waves transmitted to and from an external programmer. When an EP-study is desired the operator sets the programmer and signals are transmitted to the cardioverter/pacemaker, causing the detector to be disconnected and the stimulation pulse generator to be activated into VVT mode. Via the external programmer a sequence of pacing signals is transmitted to the stimulation pulse generator which delivers stimulation pulses to the heart synchronously with the pacing signals of the sequence. During the study the transmitting unit is also activated and transmits ECG information to the external programmer.
The sequence is mostly brief; a sequence consisting of five stimulation pulses with a time interval of 250 ms between each stimulation pulse will last just over one second. As the detector of the known cardioverter/pacemaker is disconnected during the EP-study and as the stimulation pulse generator delivers stimulation pulses controlled by the signal sequence from the programmer, the study will be fulfilled unregarding any events during the study. The stimulation pulses may not, for instance, provoke a reaction from the heart tissue and the attempt to induce a tachyarrhythmia thereby fails. It may also happen that a tachyarrhythmia with a shorter time interval than that of the sequence is induced. In such a case it would be unfortunate to deliver any further stimulation pulses to the heart.